Improvement of Pre–Twisting Fiber Bundles on Multi–Dimensional Properties of Pultrusion Composite Rods

ABSTRACT The mechanical properties of pultruded composite rods in off–axis directions are significantly inferior to those along the axial direction, which poses considerable challenges in practical structural engineering applications. For this purpose, research of pre–twisting is of interest for the multi–dimensional properties improvement of rods. This work details the fabrication, physical and mechanical property evaluation of composite rods. Pre–twisting transforms the failure mode of rods from brittle to progressive failure, such as step/vortex‐like fractures, radial deviation of fibers, etc. There is an optimal twist interval to make the multi–dimensional properties of rods reach their respective optimal state. The 30 T/m rod achieves a maximum fiber volume fraction of 74.3% (21.8%↑) with near zero porosity. It also achieves sub–high tensile strength of 3000 MPa (15.4%↑, after 60 T/m), maximum flexural properties of 1310 MPa (5.6%↑), maximum compressive properties retention rates (axial 90+ %, radial 83.4%) and shear properties retention rates (98.2%). Additionally, the 60 T/m possesses a maximum tensile strength of 3200 MPa (23.1 %↑) and low–velocity impact toughness of 285 kJ/m 2 (36.4 %↑, similar to 90 T/m with 293 kJ/m 2 ). Pre–twisting provides a cost–effective commercial possibility for improving the overall mechanical properties of composite rods.